Countershaft transmissions having a plurality of speed ratios in each direction of operation are particularly useful in the drive line of vehicles such as earthmoving wheel loaders, rubber tired log skidders, track-type tractors, and other off-highway heavy duty vehicles. Such transmissions are advantageous in that a plurality of rotating clutches and associated gears can be so positioned on the usual parallel shafts as to allow considerable flexibility in adapting them to different vehicle space requirements. A considerable number of speed ratios can also be obtained with but minor changes to the transmission, while permitting a substantial number of similar parts to be used for manufacturing economy.
For example, the following United States countershaft transmission patents are of general interest to the art: U.S. Pat. No. 3,064,488 issued Nov. 20, 1962 to A. L. Lee et al; U.S. Pat. No. 3,080,767 issued Mar. 12, 1963 to S. J. Price, Jr.; U.S. Pat. No. 3,425,293 issued Feb. 4, 1969 to H. S. Krawczyk et al; U.S. Pat. No. 3,465,609 issued Sep. 9, 1969 to J. F. Fisher et al; U.S. Pat. No. 3,710,637 issued Jan. 16, 1973 to J. F. Fisher et al; U.S. Pat. No. 3,858,455 issued Jan. 7, 1975 to R. L. Sisson et al; U.S. Pat. No. 3,913,411 issued Oct. 21, 1975 to J. J. Jameson; and U.S. Pat. No. 4,341,127 issued July 27, 1982 to E. Stodt.
While such countershaft transmissions have a considerable number of desirable features they are deficient in several other respects. One of the major problems with them is that if they are connected to the output member of the engine and/or optional torque converter assembly of the vehicle they require excessive space above the axis of the input shaft. Specifically, in some vehicular applications it would be necessary to raise the floor plates and elevate the entire operator station in order to obtain sufficient clearance above the input shaft's axis to accommodate large diameter components such as a rotating clutch thereat.
Another factor of significance is that some of these available transmissions have an excessive axial length and/or an excessive transverse width so that they cannot fit into the limited space available in a vehicle.
Furthermore, a family of countershaft transmissions is needed which can effectively match various vehicular speed requirements with the elevational drop requirements between the input and output axes. In other words, the transmission should preferably be conveniently convertible to provide one or more additional speed ratios with but minor modification. In addition to such flexibility of construction, and the need to provide both a short drop and large drop capability, the transmission should be able to provide various PTO options at the desired elevational level.
Still further, the construction of many of the prior art countershaft transmissions is excessively complex and costly. Moreover, they have other less noticeable deficiencies such as having excessive bearing speeds and/or clutch plate engagement speeds under certain operating conditions, and these deficiencies reduce the overall service life of the transmissions.
Accordingly, what is needed is a family of economical and compact countershaft transmissions that can provide at least three forward speeds and three reverse speeds, and that can maximize parts commonality and minimize the number of gears, clutches, shafts and bearings that are required. In addition to having a long service life by virtue of designing the bearings and rotating clutches such that they do not function at undesirably high operating speeds, the family of transmissions should be capable of convenient modification so that the individual transmissions can satisfy different drop height requirements as well as different numbers of speeds and speed ratio requirements and thus be adaptable to a wide variety of vehicular applications. In connection with such vehicular use, each of the transmissions should preferably be axially compact and of narrow width while having a minimum elevational clearance above the upper input axis in alignment with the engine output.